Opening a previously opened url restores the same buffer and session.

src/atom/editor.coffee

@@ -14,6 +14,7 @@ class Editor extends Template
     buffer: null
 
     initialize: () ->
+      @aceSessions = {}
       @buildAceEditor()
       @setBuffer(new Buffer)
 
@@ -24,8 +25,10 @@ class Editor extends Template
       @aceEditor.destroy()
 
     setBuffer: (@buffer) ->
-      session = new EditSession(@buffer.aceDocument, @buffer.getMode())
-      @aceEditor.setSession(session)
+      @aceEditor.setSession @getAceSessionForBuffer(buffer)
+
+    getAceSessionForBuffer: (buffer) ->
+      @aceSessions[@buffer.url] ?= new EditSession(@buffer.aceDocument, @buffer.getMode())
 
     buildAceEditor: ->
       @aceEditor = ace.edit this[0]

src/atom/project.coffee

@@ -4,17 +4,19 @@ Buffer = require 'buffer'
 module.exports =
 
 class Project
+  buffers: null
+
   constructor: (@url) ->
+    @buffers = {}
 
   getFilePaths: ->
     fs.async.listFiles(@url, true)
 
   open: (filePath) ->
-    new Buffer(@resolve(filePath))
+    filePath = @resolve filePath
+    @buffers[filePath] ?= new Buffer(filePath)
 
   resolve: (filePath) ->
-    if filePath[0] == '/'
-      filePath
-    else
-      fs.join(@url, filePath)
+    filePath = fs.join(@url, filePath) unless filePath[0] == '/'
+    fs.absolute filePath